1. Field of the Invention
This invention relates to a burner system for burning liquid fuel, or kerosene in particular, by vaporizing same so that combustion of the fuel takes place in blue flames.
2. Description of the Prior Art
In this type of burner system, a kerosene evaporator is provided and heated by an electric heater, and kerosene and primary air of a volume necessary for sustaining primary combustion are supplied to the kerosene evaporator, to vaporize the kerosene simultaneously as the air is heated. The gasified kerosene and heated air are mixed with each other and the mixture is led to flame ports for combustion.
The evaporator generally has a temperature in the range between 250.degree. and 300.degree. C. The gasified kerosene is condensed when the temperature drops and the condensate is deposited on a fuel-air mixture passage. This would cause a reduction in the proportion of the fuel in the mixture below the normal proportion, and satisfactory ignition could not be obtained. One of the factors concerned in the reduction of temperature of the gasified kerosene is the temperature of the fuel-air mixture passage. Another factor is low temperature of the primary air. To avoid the aforesaid trouble, it is customary to supply the primary air to the kerosene evaporator to heat both of them. The primary air is supplied to the evaporator so that it will serve the purpose of changing the kerosene into atomized particles. With regard to the fuel-air mixture passage, the evaporator and the premix passage are maintained in good heat conducting condition, to thereby heat the fuel-air mixture passage. Also, the structural relationship that the evaporator, fuel-air mixture passage and other parts of the burner system are kept in contact with one another is utilized for recovering heat of combustion for use in the evaporator, to minimize or eliminate the need to actuate the electric heater during steady state combustion.
Once combustion has started, the combustion produces heat which raises the temperature in the fuel-air mixture passage to a high level. It is at the time of ignition that the aforesaid trouble of condensation of the gasified kerosene occurs.
Thus, this type of burner system of the prior art has the disadvantage that pre-heating of the evaporator requires a long time at the time of ignition because the primary air and the fuel-air mixture passage should be heated to a predetermined temperature. Another disadvantage is that the burner system consumes a great deal of electric energy because the load applied to the electric heater is high due to the need of keeping the evaporator heated by the electric heater to be ready for the next following combustion cycle even when the burner system is inoperative.
From the foregoing, it will be apparent that when the fuel-air mixture passage and other parts are thermally insulated from the evaporator, it would be possible to conserve electric energy when the burner system is inoperative, but great difficulties would be encountered in igniting a fuel-air mixture.
The following references are cited to show the state of the art:
1. Japanese Patent Application Laid-Open No. 51030/79: Kerosene in constant liquid level container is led to venturi for changing the kerosene to atomized particle form by a blast of air from blower means. The kerosene in atomized particle form is caused to impinge against the gasifying surface of gasifying chamber 14 heated by a heater, and the gasified kerosene forms with air a pre-mixture of fuel and air which flows out of combustion ports to burn.
U.S. Pat. No. 4,175,919 (Japanese Patent Application Laid-Open No. 148839/77): FIGS. 6 and 7 show a burner system constituting the basic form of the embodiment of the present invention. The burner system shown is in straight line form and includes secondary air apertures in the center and slit-shaped flame ports disposed on opposite sides of the secondary air apertures for causing a pre-mixture of fuel and air to flow out therefrom.